Initial commit: migrate badge-admin from /tmp to /home/gpsystem

via HAPI (https://hapi.run)

Co-Authored-By: HAPI <noreply@hapi.run>

app/protocol/crc.py

@@ -0,0 +1,76 @@
+"""
+CRC-ITU Implementation for KKS Badge Protocol
+
+Uses CRC-16/X-25 (reflected CRC-CCITT):
+  Polynomial: 0x8408 (reflected 0x1021)
+  Initial value: 0xFFFF
+  Final XOR: 0xFFFF
+"""
+
+from typing import List
+
+# ---------------------------------------------------------------------------
+# Pre-computed CRC lookup table (256 entries, reflected polynomial 0x8408)
+# ---------------------------------------------------------------------------
+
+_CRC_TABLE: List[int] = []
+
+
+def _generate_crc_table() -> List[int]:
+    """Generate the CRC-16/X-25 lookup table for reflected polynomial 0x8408."""
+    table: List[int] = []
+    for i in range(256):
+        crc = i
+        for _ in range(8):
+            if crc & 1:
+                crc = (crc >> 1) ^ 0x8408
+            else:
+                crc >>= 1
+        table.append(crc)
+    return table
+
+
+_CRC_TABLE = _generate_crc_table()
+
+
+def crc_itu(data: bytes) -> int:
+    """
+    Compute the CRC-ITU checksum for the given data.
+
+    Uses the CRC-16/X-25 algorithm (reflected CRC-CCITT with final XOR).
+    For a KKS protocol packet this should be the bytes from (and including)
+    the packet-length field through the serial-number field.
+
+    Parameters
+    ----------
+    data : bytes
+        The data to compute the CRC over.
+
+    Returns
+    -------
+    int
+        16-bit CRC value.
+    """
+    crc: int = 0xFFFF
+    for byte in data:
+        crc = (crc >> 8) ^ _CRC_TABLE[(crc ^ byte) & 0xFF]
+    return crc ^ 0xFFFF
+
+
+def verify_crc(data: bytes, expected_crc: int) -> bool:
+    """
+    Verify that *data* produces the *expected_crc*.
+
+    Parameters
+    ----------
+    data : bytes
+        The data slice to check (same range used when computing the CRC).
+    expected_crc : int
+        The 16-bit CRC value to compare against.
+
+    Returns
+    -------
+    bool
+        ``True`` if the computed CRC matches *expected_crc*.
+    """
+    return crc_itu(data) == (expected_crc & 0xFFFF)